The present invention relates to a communication terminal device which is driven normally by a commercial power source and capable of making telephone communication, using a power supply provided on the side of communication lines at a power stoppage, and a dialing key.
A communication terminal device such as a facsimile device, using a commercial power source, have become widespread. The terminal device of some type is provided with both the function of using a commercial power source (facsimile communication, message record/reproduction, etc.) and the function of a normal telephone set.
Among these terminal devices, there is provided a type of terminal device in which both of the functions as mentioned above are not operated during power failure, and a type of terminal device in which the function of using a commercial power source is not available but the function of a normal telephone set is available. In the latter type of terminal device, it is necessary to provide a safety circuit and to separate the commercial power source electrically, and upon power failure, a telephone set circuit is separated for example through a relay to supply power to the telephone set circuit from the communication line. A ten-key unit of the terminal device which dials a telephone number has a switch which sends a signal to a microcomputer which operates with the commercial power source and a switch which sends a signal to a circuit operating with the communication lines. Depression of one button of the ten-key unit operates those two switches to switch the circuit concerned, depending on whether power supply to the terminal device has now been stopped or not in order to cope with the power stoppage.
As shown in FIGS. 10 and 11, a conventional dial section is provided with a panel 1 and buttons 2 attached to the panel 1 so as to protrude partially from the panel. When a button 2 is depressed, a contact 3 made of an elastic material such as rubber is collapsed to come into contact with a printed wiring board 4. The contact 3 has two circular electrodes 5 printed with electroconductive ink on a lower surface thereof such that an electric current can flow across those electrodes. The electrodes 5 come into contact with a switch 6 formed in a pattern on the board 4 to switch on the switch 6.
For the printing process for the formation of the switches, that system as just mentioned above is capable of forming both the first and second switches simultaneously, so that the cost taken for carrying out that process is very low, advantageously.
However, the telephone dial requires 12 switches and a double-sided printed wiring board 4 is required for forming wiring patterns one on each of both the surfaces thereof to thereby form 12 switches independent of a circuit involving the 12 dial switches because wiring for the individual switches is difficult if the wiring pattern is formed on only one surface of the printed board. This would increase the cost of the device manufacture.
When the button 2 is depressed at one edge, it would be pushed obliquely. Thus, the phenomenon is likely to occur that only one of the two switches is switched on while the other is not switched on. In order to avoid such situation, limitations to design of the device would occur. For example, the finish of the panel 1 which guides the sliding movement of the button 2 would require high accuracy, undesirably.
Further, it is necessary to provide sufficient length intervals for electrical insulation of conductive patterns from patterns used for power failure. In a large sized switch, particularly the problem as mentioned above often happens. There also arises a problem of restriction on design.